1. Technical Field
The disclosed concepts relate to a light quantity distribution control element and a light quantity distribution control lens used preferably to correct non-uniform light quantity in optical scanning devices or the like, and an information recording/reproducing apparatus, an image pickup device and an optical scanning device using the same, and an image-forming apparatus using the optical scanning device.
2. Description of the Background Art
A number of optical scanning devices used in laser beam printers or the like include a semiconductor laser as a light source, a first imaging optical system for imaging light flux from the light source linearly on a rotary polygon mirror in order to correct the pyramidal error of the rotary polygon mirror, a polygon mirror as the rotary polygon mirror and a second imaging optical system for imaging uniform spots at a constant velocity on a photoconductor drum, which is a surface to be scanned.
In a conventional optical scanning device, an effective aperture in the main scanning direction is provided before the polygon mirror, and this is a underfilled type in which a line image that is smaller than the width in the main scanning direction of the deflection reflective surface of the polygon mirror is formed. However, in order to increase the number of the deflection reflective surface of the polygon mirror, it is necessary to increase the inner diameter and thus it is difficult to increase the speed. Therefore, optical scanning devices of overfilled type in which a line image larger than that in the main scanning direction of the deflection reflective surface of the polygon mirror is formed and the deflection reflective surface of the polygon mirror is used as the effective aperture in the main scanning direction have been proposed. However, in such a case, the width of the defection reflective surface of the polygon mirror is smaller than the width of the light flux having a spatial intensity distribution, so that the light quantity directed to the periphery is smaller than the light quantity directed to the vicinity of the center in the longitudinal direction of the photoconductor drum. Therefore, the light quantity on the photoconductor drum becomes non-uniform, so that it is difficult to obtain high quality recorded images.
Therefore, methods for correcting non-uniformity of light quantity have been proposed, such as a method of providing a filter for cutting by coating a portion having a strong beam intensity distribution with a metal film between the light source and the polygon mirror, and a method of coating a fθ lens so as to provide a transmittance distribution such that the light quantity distribution becomes uniform (e.g., see JP8-160338A and JP2001-290093A)
However, with the above-described configurations, the cost is increased and variation in light quantity also is increased.